Research Of Ground Fault And Sub-health In Photovoltaic System

The large amount of greenhouse gases from huge fossil energy consumption have caused the deterioration of the environment,which have forced human beings to develop and utilize new energy resources and improve the energy structure.Solar energy is regarded as one of the best alternatives to fossil energy in the future because of its green and sustainable development.In recent years,the installed capacity of solar energy systems continues to grow,and the wide application of solar photovoltaic power generation is accompanied by efficiency,safety and other issues.In this dissertation,the characteristics and effective detection of common ground fault and high resistance line fault in photovoltaic system are studied.The main work is as follows:(1)Aiming at the problem of ground fault in photovoltaic system,a ground fault detection method based on spread spectrum time domain reflectometry(SSTDR)is proposed because of the blind detection area of conventional methods.By comparing the processing results of SSTDR autocorrelation value with or without ground fault,the detection of ground fault is realized.On the basis of theoretical analysis and experimental platform,the feasibility and validity of the proposed method in varied ground conditions with different irradiance,different ground resistance and double ground fault is verified by experiments.(2)In order to further locate the ground fault of the photovoltaic system,a method based on high frequency signal injection is proposed.According to the variation of impedance amplitude of PV strings at resonance frequency point,the ground fault location can be realized.This method has the advantages of small calculation,fast positioning speed and high positioning accuracy.The experimental results show that the method can effectively locate the ground fault under different illumination conditions and different ground fault resistances.(3)The insulation of photovoltaic system will be damaged due to the bad working environment,drastic changes in temperature and humidity,and natural aging,which may lead to high impedance line fault.In this dissertation,the high impedance line fault is defined as the sub-healthy states of photovoltaic system,which is difficult to detect by conventional methods.Through modeling and simulation of photovoltaic array,the change of fault current when line fault occurs is analyzed,and a sub-health state detection method based on voltage division is proposed.The correctness and effectiveness of the method is proved by experiments.